[media] vb2: fix nasty vb2_thread regression

The vb2_thread implementation was made generic and was moved from
videobuf2-v4l2.c to videobuf2-core.c in commit af3bac1a. Unfortunately
that clearly was never tested since it broke read() causing NULL address
references.

The root cause was confused handling of vb2_buffer vs v4l2_buffer (the pb
pointer in various core functions).

The v4l2_buffer no longer exists after moving the code into the core and
it is no longer needed. However, the vb2_thread code passed a pointer to
a vb2_buffer to the core functions were a v4l2_buffer pointer was expected
and vb2_thread expected that the vb2_buffer fields would be filled in
correctly.

This is obviously wrong since v4l2_buffer != vb2_buffer. Note that the
pb pointer is a void pointer, so no type-checking took place.

This patch fixes this problem:

1) allow pb to be NULL for vb2_core_(d)qbuf. The vb2_thread code will use
   a NULL pointer here since they don't care about v4l2_buffer anyway.
2) let vb2_core_dqbuf pass back the index of the received buffer. This is
   all vb2_thread needs: this index is the index into the q->bufs array
   and vb2_thread just gets the vb2_buffer from there.
3) the fileio->b pointer (that originally contained a v4l2_buffer) is
   removed altogether since it is no longer needed.

Tested with vivid and the cobalt driver.

Cc: stable@vger.kernel.org # Kernel >= 4.3
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index ef03ae56b1c1..8a0f55b6c2ba 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -533,7 +533,8 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
 		const unsigned int requested_sizes[]);
 int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
 int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb);
-int vb2_core_dqbuf(struct vb2_queue *q, void *pb, bool nonblocking);
+int vb2_core_dqbuf(struct vb2_queue *q, unsigned int *pindex, void *pb,
+		   bool nonblocking);
 
 int vb2_core_streamon(struct vb2_queue *q, unsigned int type);
 int vb2_core_streamoff(struct vb2_queue *q, unsigned int type);